In many applications of biological and biochemical research, it is important or essential to obtain purified DNA from samples. Frequently, an investigator must obtain a pure sample of plasmids or nuclear DNA, e.g., in assaying for genes which express a particular protein, to determine whether or not a particular sample of cell has been transfected by a foreign gene, and so forth.
The standard methodology for extracting DNA, as explained, e.g., by Herrmann, et al., Meth. Enzymol 152: 180-183 (1987), involves differentiated solvation of the DNA and the non-DNA material, using phenol and chloroform. In this standard methodology, following a series of preparative steps the DNA containing sample is mixed with an organic solvent, such as phenol, or preferably, an equal mixture of phenol and chloroform. Proteins denature and enter the organic phase (phenol), or precipitate at the interface of the organic and aqueous phases. The aqueous phase contains the DNA. Mixing this with alcohol causes precipitation of the DNA which can then be spooled. See, e.g., Rodriquez, et al., Recombinant DNA Techniques: An Introduction (Benjamin/Cummings Publishing Co., Menlo Park, 1983), pg. 38.
While the aforementioned phenol/chloroform extraction method is standard in the art, it is far from ideal. Phenol and chloroform are both toxic chemicals, implicated as potential carcinogens, so it is of course desirable that the investigator not contact these. However, the standard protocols for separation require aspiration of the aqueous DNA containing solvent. Pouring the material from the second solvent is not an acceptable alternative, because the barrier between phenol and chloroform is not very stable, and contamination is inevitable. Further, at the interphase between the chloroform and phenol layers, it frequently becomes very difficult to separate the DNA found at this point. As a result, yields are low, or, at the least, not as high as they can be.
Thus, it is desirable to have available a method which permits the investigator to carry out DNA extraction and/or separation which does not require aspiration. Further, it is desirable to have a method available which, in addition to being safe to us, results in high yields of DNA.